1. Technical Field of the Invention
This invention relates to a press machine having a frame which is C-shaped in side elevational view, a bolster which is mounted on a bed of a lower jaw portion of the frame, and a slide which is mounted on an upper jaw portion of the frame. More particularly, this invention relates to a press machine whose side frames are reinforced by reinforcing members.
2. Discussion of Related Art
A prior art example of a press machine i to which the present invention relates is shown in FIG. 1. A frame 2 of the press machine 1 is C-shaped in side elevational view, and has a lower jaw portion with a bed 4 supported thereon, and an upper jaw portion with a slide 5 and a driving unit for driving the slide 5 supported thereon. The arrangement is made such that when the slide 5 is lowered by rotation of a main spindle, a workpiece (not shown) positioned on a lower die 7 mounted on a bolster 4a resting on the bed 4 is punched by an upper die (punch) 6 fixedly secured to the slide 5. In FIG. 1, reference numeral 3 denotes a front side plate of the frame, and reference numeral 8 denotes a side frame.
In the above-mentioned prior art press machine 1, to suppress or reduce the vibration of the frame 2 or the level of noise generated by the press, for example, either (1) a vibration damping material is mounted on the surface of the frame, or (2) the whole press machine is surrounded by a box to isolate the noise. (Refer, for example, to "Examples of Measures for controlling Noise generated by Press Machines", collection of lectures and thesis on technique presentation conferences issued by Japanese Noise Control Engineering Society, P141, September 1989).
Further, as shown in FIGS. 2 and 3, a third prior art alternative (3) for reducing or suppressing the vibration of the frame or the level of noise generated includes mounting an L-shaped reinforcing plate-shaped member 9 on the inner surface of each of the side frames 8.
The problem with mounting a vibration damping material on the surface of the frame, as in the abovementioned case (1), is that it causes an increase in the weight and cost of the entire press machine. For effective vibration damping, the thickness of the vibration damping material must be at least equal to or more than that of the frame, so that if the thickness of the frame is 22 mm, for example, then the total thickness of the frame and the vibration damping material becomes about 50 mm, thus increasing the weight of the entire press machine, giving disadvantages in terms of cost and practicality.
Further, where the whole press machine is surrounded by a box, as in the above-mentioned case (2), other problems exist relating to press operation, cost and the need for increased working space in factories.
Still further, in the above-mentioned alternative (3), as shown in FIGS. 2 and 3, because the plate-shaped member 9 is fixedly secured to each of the side frames 8 as the reinforcing member thereof, the reinforcing effect for preventing the opening formed between the upper and lower jaws of the frame from flaring was limited. Further, the prior art reinforcing member 9 mounted on the side frames 8 so as to extend upwards from the upper jaw portion is inefficient as a reinforcing member since only a small loading is applied to this portion.
A fourth alternative (4) for reducing or suppressing the vibration of the frame is described in Japanese Patent Publication 55-46399. This alternative uses a pair of tie rods 2 extending between opposite side frames 1, 1' of a press machine. The tie rods 2 are fixed to each side frame by means of a nut 3 and a load plate 4, 5. A preload is applied to the tie rods 2 to reduce or suppress at least certain kinds of vibrations occurring in the side frames during operation. The '399 device uses a vibration damping technique which relies on an increased stiffness of the structure to reduce the vibration amplitude. The vibration energy itself is not dispersed into another form of energy (e.g., heat)--it is just converted into a different amplitude.
The '399 device has significant drawbacks. The arrangement of the tie rods 2 between the side frames substantially limits or interferes with the arrangement of a device or mechanisms disposed inside the press machine. Moreover, the preload strain applied to the press body of the device by the tie rods 2 is disadvantageous because it creates damaging stress in the side frames and tends to disorder the positioning accuracy of the mechanisms within the frame. Thus, the use of the tie rods requires readjustment of the mechanisms for proper performance after securing the tie rods, thereby creating an additional inconvenience. Further, the vibration damping effects of the tie rod arrangement of the '399 device is less than satisfactory because the arrangement is not effective against antisymmetric vibrations of the side frames (i.e., both side frames moving in the same direction in the same phase) during operation of the press machine.